Copper base alloys have been extensively utilized in tubing for heat exchanger applications. These alloys, in particular the copper-nickel alloys, have found wide acceptance due to their good balance of corrosion resistance and mechanical properties. In particular, such alloys as Alloy 706 and 715 (containing, respectively, 10% and 30% nickel in a copper base) have found wide acceptance in surface condenser heat exchangers utilized by power generating plants. These alloys, although widely used, do present difficulties of their own. In particular, at least 10% nickel is usually necessary in the alloys to achieve good corrosion resistance. This tends to make the alloys quite expensive and therefore uncompetitive with certain other non-copper alloy systems. The initial corrosion rates for these copper-nickel alloys also tend to be quite high until a protective film has had a chance to form on the tubing surface made from such alloys. This high initial corrosion rate raises the possibility of copper being released to the environment and in particular to potable water flowing through tubes made from such alloys. The presence of ionic copper in industrial effluents is thought to be harmful to some aquatic species. Therefore, research has been done into various alloy systems to determine an alloy which reduces such copper release without being overly expensive.
Various alloy systems have been developed to overcome the high cost of the copper-nickel alloy systems. These alloy systems have generally not been able to provide the high corrosion resistance properties of the copper-nickel alloys in heat exchanger applications. Alloy systems have been developed for their corrosion resistance and strength properties which utilize varied alloy additions for such properties. For example, U.S. Pat. No. 3,937,638 utilizes various additions of nickel and tin to a copper base to provide increased strength and corrosion resistance properties. This patent also mentions that various other additions such as zinc, manganese, silicon, phosphorus, lead and chromium may also be added to the alloy system. This alloy system undergoes a specific working and heat treating operation to achieve these properties.
Another alloy system containing manganese, nickel and aluminum in a copper base and also tin, nickel and aluminum in a copper base is taught in "Properties of Some Temper-Hardening Copper Alloys Containing Additions of Nickel and Aluminium" in the Journal of the Institute of Metals, Volume 52, No. 3 (1933) on Pages 153 to 184. This particular article nowhere teaches that these alloy systems may be utilized for their corrosion resistance properties specifically in tubing applications. None of these references, either the U.S. patent or the article, disclose the particular alloy system and accompanying use which will be disclosed in the present specification.
Therefore, it is a principal object of the present invention to provide an alloy system which is highly resistant to corrosion without being high in cost.
It is a further object of the present invention to provide an alloy system as aforesaid which provides increased resistance to corrosion in potable and brackish water applications compared to commercially available corrosion resistant alloys.
It is a further object of the present invention to provide an alloy system as aforesaid which exhibits a low initial corrosion rate to minimize soluble copper release to the environment on start up of tubing systems.
It is yet a further object of the present invention to provide an alloy system as aforesaid which retains single phase properties within the alloy structure after processing to increase corrosion resistance properties.
Further objects and advantages of the present invention will become apparent from a consideration of the following specification.